Sorry to hear you feel alone and lost
how old is your little boy?
My little boy is 6 weeks and I'll be honest and say it's only this week that I've started to feel ok and that I can cope.
I love him to bits but the first 4/5 weeks were really tough as it's such a big change (plus I couldn't get out as had a c-section).
I had a bad cold still on Mon so we stayed in but since then we've been somewhere every day which I've found has really helped. Can you get out each day?
We did the following;
Mon - home as I had a cold but dh finishes at lunch.
Tue - went to Tesco
Wed - my postnatal check at GP combined with a stroll around the village
Thur - popped into work to show ds off 
Fri - took ds to see my nan and aunt.
So a lot of my week was doing things that had to be done but just leaving the house was great.
Do you have any friends or family you can visit?
Are there any groups in your area? I plan to try some next week.
Can you wander round the shops/park/town?
Perhaps ask your hv for local groups/activities?
Good luck - you're not a bad mum it just takes time to find your feet xx